Method of making magnetic cores



March 4, 1952 G. G. SOMERVILLE 2,588,173

METHOD OF MAKING MAGNETIC CORES Filed Aug. 24, 1948 Inventor: Gareth. G,Semen/Hie His Attorney Patented Mar. 4, 1952 METHOD OF MAKING MAGNETICCORES Gareth G. Somerville, Pittsfield, Mass, assignor toGeneralElectric Company, a corporation of N ew York Application August24, 1948, Serial No. 45,833

1 Claim.

This invention relates to magnetic cores and more particularly toimprovements in wound cores and the method of making the same.

Conventionally, magnetic cores for induction devices are constructed ofpunched or cut laminations which are stacked one above he other to formthe core structure. This methodhas the inherent disadvantage of beinglimited to cores which have laminations of substantial thickness sinceit is difiicult to satisfactorily punch or out very thin magneticmaterials. By very thin is meant materials having a thickness of lessthan 3 mils. One of the only ways cores formed of such thin layers canbe satisfactorily constructed is by winding them from strip material.Since a rolled steel having a most favorable magnetic direction in thedirection of the grain may be used in forming such a core, substantiallylower core losses may result due to the fact that the flux flowscontinually along the path of least magnetic losses. After the core hasbeen wound and properly annealed, it is often necessary to cut the coreto allow for the mounting of the associated coils. It is the commonpractice to cut the core in half, by any suitable means, and after thecoils are mounted to orient the two halves in adjacent abuttingrelationship to one another. The use of a butt joint increases thereluctance of the core by allowing the formation of an air gap betweenthe two core halves. If the two core halves are maintained in intimatemagnetic contact by means of lapped joints, the reluctance of themagnetic core is decreased since there is no unbridged air gap present.

In accordance with this invention, there is provided a preferably woundmagnetic core having two halves which are lap-jointed together and theuse of butt joints is completely eliminated. This is accomplished byusing a method of construction which allows the strips of conventionallycoated magnetic material from which each half of the core is constructedto be interleaved one with the other.

It is an object of this invention to provide a new and improved magneticcore.

Another object of this invention is to provide a novel method of makinga magnetic core.

A further object of this invention is to provide a new and improvedmagnetic core formed in two overlapping interleaved parts.

Still another object of this invention is to provide a new and improvedmagnetic core which utilizes a plurality of lapped joints and therebyachieves lower magnetic reluctance.

A further object of this invention is to provide a lap-jointed magneticcore of very thin layers of magnetic material whose method ofconstruction eliminates the use of punches and dies.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claim.

In the drawing, Fig. l is a perspective view of an induction apparatushaving a core constructed in accordance with this invention. Fig. 2illustrates the first step in the method of making a core in accordancewith this invention. Fig. 8 is a perspective view, and Fig. 4 a frontelevation illustrating successive steps in the method of making the coreshown in Fig. 1. Fig. 5-is a front elevation of an alternative method ofcore construction.

Referring now to the drawing, there is shown in Fig. 1 anelectromagnetic induction apparatus I having a core 2 constructed inaccordance with this invention and having mounted on it the coils 3 andl which may serve as the primary and secondary of a transformer. Thefirst step in the method of constructing core 2 is shown in Fig. 2,wherein a continuous strip of magnetic material 5 is wound on arotatable axle or mandrel 6 which has a substantially rectangular shape.It should be noted that a plurality of magnetic strips may be woundsimultaneously on the mandrel 6, so that for each rotation of themandrel 6, a plurality of layers is formed. In Fig. 2, it can be seenthat the rectangular shape of the mandrel 6 is imparted to the core asit is wound, thus forming the sides 1 and 8 and the ends 9 and I0. Asthe core 2 is wound upon the mandrel 6 to form a closed loop, spacers Hmay be placed between individual layers or groups of layers of the corematerial, as shown at the ends 9 and Ill. The cross-sectional height ofthe spacers II, or the thickness of each spacer times the number ofspacers used, should be such as to be approximately equal to thecross-sectional height 01', as is generally known in the art, the buildof the core 2. It has been found advantageous to wind 3 or 4convolutions of the core 2 before inserting a spacer I I; the spacerbeing of a thickness equivalent to the combined thickness of theconvolutions plus approximately 10%.

After the core 2 has been wound on the mandrel 6, it may be placed in aclamp to accentuate its rectangular shape. It is then annealed at a hightemperature in a protective atmosphere which is generally hydrogen. Thisannealing process not only reduces the strains present in the steel dueto rolling and winding, but it also one half of the core 2, the coil 3is wound and on the remaining half is wound the coil 4.

In finally assembling the core 2, the two halves l3 and M are broughtinto intimate magnetic contact by interleaving each layer or group oflayers and achieving a plurality of lapped joints by placing the layersof the core in the spaces which were provided by the spacers II. Theinduction device I is permanently clamped as a unit by any suitablemeans, such as a clamping band 15, which may be wound around theperiphery of the core 2 and spot welded at the point I6.

Fig. 5 shows an alternative method of winding a core I! which eliminatesthe use of separate spacer material and achieves the spacing betweenlayers of the core by crimping the continuous strip of magnetic materialor by winding it back upon itself at each end, as shown by I8. Thus,when the core is out, small U-shaped pieces of magnetic material may beremoved leaving spaces similar to those provided by the spacers II inFig. 1. Separate means not illustrated in the drawing may be provided tocrimp or bend the magnetic strips back upon themselves. In Fig. 5, eachsuccessive layer of magnetic material is shown bent back upon itself atboth ends of the core 11. In actual practice, it has been found mostconvenient to wind at least three layers of the strip materialsimultaneously and these three layers are bent back upon themselves.

While there have been shown and described particular embodiments of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from theinvention and, therefore, it is aimed in the appended claim to cover allsuch changes and modifications as fall within the true spirit and scopeof the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

The method of making a wound core having a plurality of lapped jointswhich comprises winding a strip of magnetic material into a closed loophaving any desired number of layers, crimping said magnetic materialback upon itself during the winding operation so as to cause successivelayers of said closed loop to be separated at two diametrically oppositezones of said loop by an amount equal to at least the thickness of oneof said layers, the crimped portions of said magnetic material all beingaligned with respect to a plane extending transversely through said loopcutting through said closed loop and through all of the crimped portionsof said loop along said plane, removing the resulting crimped portionhalves and interleaving the ends of the layers of the loop sections thusformed to produce a core having a plurality of lapped joints. 1

GARETH G. SOMERVILLE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,797,807 Swendsen Mar. 24, 19311,933,140 Gakle Oct. 31, 1933 1,992,822 Granfield (A) Feb. 26, 19352,142,066 Eppelsheimer Dec. 27, 1938 2,330,824 Granfield (B) Oct. 5,1943 2,387,099 Vienneau Oct. 16, 1945 2,393,439 White Jan. .22, 19462,456,461 Dunn Dec. 14, 1948 2,478,030 Vienneau Aug. '2, 1949 2,489,625Dornbusch Nov. 29, 1949 2,516,164 Vienneau July 25, 1950

